Throughout the arts there are many instances where two liquids must be proportionally combined and/or mixed. Still further, in many such instances, one of the liquids is provided or supplied in a non-pressurized or pressure neutral condition and the other liquid is supplied under pressure. In such instances, aspirators are commonly employed to proportionally combine and/or mix the two liquids. The liquids supplied under pressure are utilized as motive liquids and when conducted through the aspirators, draw the pressure neutral liquids into the aspirators to combine with the motive liquids flowing therethrough.
The ordinary aspirator suitable for proportionally combining pressure material and pressurized liquids is characterized by a structure defining an elongate aspirating chamber with an open end and a closed end, a high pressure nozzle passage of reduced diameter, concentric with and opening at the closed end of the aspirating chamber and connected with a supply of motive liquid and a low pressure inlet port communicating with the mixing chamber between the ends thereof and connected with the supply of pressure neutral liquid. The nozzle passage directs a high velocity stream or jet of motive fluid longitudinally through and from the open end of the aspirating chamber.
The jet of motive liquid establishes a minus pressure in the aspirating chamber. That minus pressure draws the pressure neutral liquid into the chamber, through the port to combine with the motive liquid.
The effectiveness and/or efficiency of aspirators of the general character referred to above varies greatly. The construction of such aspirators is extremely simple and easy to make and their design and resulting efficiency, is generally arrived at by empirical methods of making, adjusting and testing some basic aspirator structures until a satisfactory result is attained.
As a general rule, where aspirators of the character referred to above are used, the outlet end of the aspirating chambers open into large diameter liquid conducting containers which are such that no adverse restriction of flow and/or back pressures are created downstream of the aspirating chambers. That is, the liquids are "dumped" free from the aspirators.
One special type or class of machine in which proportional mixing liquid aspirators are widely used are those beverage dispensing machines which are characterized by large upwardly opening beverage supply tanks in which beverages established of proportionally mixed water and liquid beverage concentrates are stored and from which the beverages are dispensed. For merchandising and aesthetic purposes, the supply tanks of such machines are transparent and such that the beverage can be temptingly viewed by viewed by perspective purchasers. Such tanks are generally and preferably kept at least threequarters full and the beverages are caused to circulate to keep their ingredients well mixed and to enhance the aesthetics thereof.
In such beverage dispensing machines, the aspirators are operated intermittently to maintain the beverage in the tanks at desired levels. The high pressure nozzle passages of the aspirators of such machines are suitably connected with pressurized municipal water supply systems or the like and the low pressure inlet ports are suitably connected with pressure neutral supplies of liquid beverage concentrates adjacent to or remote from the aspirators and/or the beverage supply tanks.
In machines of the character referred to above, it has been clearly established that the aspirators are most conveniently and effectively carried by covers for and overlying the open tops of the supply tanks so that the beverage mixed therein and dispensed thereby simply pours or dumps downwardly into the tanks to combine with the existing supply of beverage therein. Another reason for locating the aspirators at the tops of the supply tanks resides in the fact that the aspirators must be above the liquid level in the tanks or otherwise isolated therefrom so that when the aspirators are not in operation, the possibility or likelihood of the aspirators functioning to syphon beverage from the tanks and back into the concentrate and/or water supplies is avoided.
Further, in such beverage dispensing machines, the mixed concentrates and water are often such that if freely dispensed from the aspirators into the tanks, above the beverage levels in the tanks, the liquids splash about in an unsightly and undesirable manner, generating undesirable noise and often creating heads of foam on the beverage in the tank which are not only unsightly but which tend to leak or flood from the tops of the tanks and create objectionable clean-up and maintenance problems.
As a result of the foregoing, the prior art have provided aspirators with vertical delivery tubes with upper ends communicating with the outlets of the aspirating chambers of the aspirators and which depend into and open within the volume of beverage in the supply tanks. Such delivery tubes prevent splashing, reduce undesirable noise and substantially eliminate the generating of foam or the like. However, in order to prevent back syphoning the liquid beverage through the delivery tubes and their related aspirators, the delivery tubes must be provided with anti-syphon vents or ports in the sides thereof, above the liquid level in the supply tanks. If such ports are made too small, they tend to become plugged and/or stopped up by the syrupy and oftentimes fruit pulp ladened beverage concentrates and are rendered ineffective. If such vent openings are made sufficiently large so that they will not become plugged or fouled, they are, as a general rule, so large that they afford less resistance to the flow of beverage through them than is afforded by the portions of the tube below them and the beverages tend to flow out through the vent ports and create all of those problems and adverse effects the delivery tubes are intended to eliminate.